It has been known for three decades that bone structures have bioelectric properties. It is known, for example, that bones tend to be electronegative in areas of compression and electropositive in areas of tension, and that areas of active growth and repair tend to be electronegative. Many workers have demonstrated the phenomenon of electric current stimulated osteogenesis at the cathode. Electric currents, both AC and DC, including pulsating DC, in the range of from about 10 to 100 microamperes is known to stimulate bone growth in some but not necessarily all subjects. The literature on this subject is extensive, see, e.g. Spadaro JA: Electrically Stimulated Bone Growth in Animals and Man, A review of the Literature, Clin. Orthop. 122: 325, 1977.
Implantable electric current bone growth stimulator devices have been reported, see, e.g., U.S. Pat. Nos. 3,745,995; 3,783,880; 3,890,953; 3,915,151; 3,968,790; 4,011,861; 4,052,754; 4,306,564; 4,313,438; 4,315,503; 4,333,469 and 4,414,979. Prostheses having electrically stimulated bone growth devices have also been proposed; see, e.g., U.S. Pat. Nos. 3,964,473; 4,195,367; 4,214,322 and 4,216,548. Non-invasive bone growth stimulators, see, e.g. U.S. Pat. Nos. 4,056,097; 4,066,065; 4,153,060; 4,175,565 and 4,244,373, and bone growth stimulators with specific current and voltage patterns, see, e.g., U.S. Pat. Nos. 4,105,017; 4,266,532; 4,266,533; and 4,315,503, have been described. Semi-invasive bone growth stimulators have also been disclosed, see, e.g., Zimmer, "The Alternate Treatment of Fracture Nonunion, Electrical Stimulation to Induce Osteogenesis, Zimmer USA, Warsaw, Ind. 46580, September 1979 revision, and U.S. Pat. Nos. 3,842,841 and 3,918,440.
U.S. Pat. No. 4,026,304 reviews the state of the art and early developments and is incorporated herein by reference. This patent also discusses the problem of polarization and proposes, as a solution, an implantable source of electric potential to generate a train of electric pulses.
U.S. Pat. No. 3,893,462 discloses another method of bone growth stimulation utilizing electrical signals undulating in both the positive and negative directions in an asymmetric manner reactively coupled to the bone.
The general approach in the prior art has been to provide an electric current bone growth stimulator separately from any external fixation which may be used. While efforts have been made to avoid or mitigate the problem of polarization which results when current flows in a given direction through an electrode. The present invention addresses the problems of external fixation and bone growth stimulation, including the problem of polarization.